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Performance Of The Beijing Pulsed Variable-energy Positron Beam

机译:北京脉冲变能量正电子束的性能

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In order to study the depth-dependent characteristics of open-volume defects in thin surface layers, the variable-energy positron lifetime spectroscopy (VEPLS) has been enabled by pulsing a continuous positron beam. The buncher is a quarter-wave coaxial resonator and the RF-signal is fed in by a coupling loop with a frequency of 149.89 MHz and the reflection factor of 0.05 measured by a Network Analyzer. Three synchronic signals with their phases and amplitudes adjusted independently are supplied for start signal of the positron lifetime measurement and the power signal by an electronic system. The stop signal is derived from a detector, a BaF_2 scintillator coupled to a photomultiplier-tube (Hamamatsu). The time resolution of 295 ps (FWHM) was achieved for a Kapton film and a Ti sample at positron energies in the range between 1 keV and 30 keV.
机译:为了研究薄表面层中开孔缺陷的深度相关特性,通过对连续的正电子束施加脉冲来启用可变能量正电子寿命谱(VEPLS)。聚束器是一个四分之一波长同轴谐振器,RF信号由耦合环馈入,该耦合环的频率为149.89 MHz,网络分析仪测得的反射系数为0.05。通过电子系统提供三个同步信号,分别调整其相位和幅度,以用于正电子寿命测量的启动信号和功率信号。停止信号来自检测器,BaF_2闪烁体耦合到光电倍增管(滨松)。在正电子能量为1 keV到30 keV的范围内,Kapton膜和Ti样品的时间分辨率为295 ps(FWHM)。

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